1. Field of the Invention
The present invention relates generally to measuring the tension on cables, more particularly to measuring the tension of fixed cables, and most particularly to measuring the tension of fixed cables on aircraft.
2. Description of the Related Art
Many aircraft employ numerous cables to make very sensitive flight related adjustments to operate the aircraft, such as to control surfaces, etc. Precise measurement of cable tension loads in real-time to ensure accurate aircraft operation related to such cables can significantly increase the effectiveness of such cables. Currently available cable tension monitoring devices cannot be employed for this purpose.
Devices for measuring the tension placed on wires and cables, known as tensiometers, have been used for many years in industries as varied as yarn manufacture to oil well drilling. Many tensiometers are designed so that the cable runs through the device and the tension on the cable as it travels is measured. Such devices are employed to make yarn or in industries that use cables that run through pulley systems to operate machinery. Such tensiometers cannot be employed for measuring tension on cables that are fixed at both ends, such as those used on aircraft.
Other tensiometers have been developed to work on such fixed cables, but have other inherent problems that would obviate their use on aircraft cables. For example, U.S. Pat. No. 4,989,450 discloses a hand held cable tensiometer that attaches to two points on a cable. However, this cable tensiometer employs a load cell to measure cable tension, which would be too large and heavy for operation in a flight environment.
U.S. Pat. Nos. 5,728,953 and 6,343,515 disclose cable tensiometers that use a bending beam configuration so that the requirement to employ a separate measuring device, such as a load cell, is not needed. These devices measure the tension in a cable by fixing the cable to the devices, which employ a fixed structure, and creating an angle in cable. When tension is placed on the cable, the angles causes the fixed structure to bend. The bending is measured via small strain gages that are also affixed to the fixed structure to obtain the tension placed on the cable. However, the U.S. Pat. No. 6,343,515 patent employs a separate tubular structure to hold the cable and deflection blocks to create the angle in the cable and the U.S. Pat. No. 5,728,953 patent employs a spacer block to create the angle in the cable, which increases the weight of the devices to a point where they could not be used in a flight environment. Further, the U.S. Pat. No. 6,343,515 patent clamps the cable to the tubular body and the U.S. Pat. No. 5,728,953 clamps the cable to the fixed structure. Such clamping creates significant friction on the cable and dramatically decreases the precision of the devices.
Therefore, it is desired to provide a cable tension measurement device for fixed cables that is precise, repeatable, and can operate in an aircraft flight environment.